From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.251 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793516380; b=Iwba1PxuXkRyL0YKsn81/L2UEMZm7p4Y/P240dAXo1LWaFWS6QTahibUB8Z/5vbTUHkX DLjZWLSoEFCJuokAZifDknGRf2fkR2sQVESaOpzXeKKHabQ67oOTIOPqVPme/ETipXI4z Mh++fyismb/d82Lf/4m54tyFKHwcjaIgqPaCaHBdSS99yyQW8BqJ35yOY97Bbxikh3IcW iCrNNHkAA+0jRe5mSlxCL1SDL94JSz7cKC/8ynhmrS+bTySmzR6S1FToEEqeXhnxk2ENU pgWGJ7h6FmqYGlpfkZ3RO5OSVTSe4XhA88OoCFYNCIxbZYgDi/ZsiugT16eeMYIXCaA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793516380; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=YeIoxROzkAdhFI4Ar5AnwjuAhq4OI4vjyPjDPC2k3nU=; b=mTCamxan/dbUmHEs5ZvdONC2+e2EO0oZcXTR2mlsbRG4h8NzhD6ktPOPelpcwrTrNm3E qFmGjfBsFXWhX4/k83EpgLzCmO5gTQHfg6Oe9nnp/qXuQ0mkbB9OH/9YG7kOKdDLhzPjn J+u1uWgprkc4/WgDbguEFxoT83AY7jPWHaz2NNYLS+9UpXWg/UUFQNESo8XmDhTdqA8uv VHktEaiHTNfsPFeLegttIl0auKM46enA/ldawCHeVSSCyStqiae+PF03aFodcogQMrFuv UjTtu0xHLH29Ge4Sj0bfARkuziyOtAtwdv4eqo3yxLdaAtTs//IUrzG27NxL4wCiQoA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=KsW8zLjF; arc=none smtp.remote-ip=95.215.58.251 Received: from mta1.migadu.com (out-251.mta1.migadu.com [95.215.58.251]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DDC11606A325 for ; Sun, 1 Nov 2026 06:59:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org DDC11606A325 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=KsW8zLjF X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=uSVvmFSAIOfOrJ9voHYtRM47z6sjBlD60gkSR70O4ak=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793516378; v=1; x=1794121178; b=KsW8zLjFG6M6V/qOXwO1HZPLeKqacZiKOP5IsUbZakyHpCXTx1jy7XHWmVpu8XNRaUsNOfim g+U7Vd3AgTiyqqLSXaNqtpgJesGIv3jJgLv0z8tJQXejBjLrSE3sRoEG2RGROrD6rXAN1Z6ZR+f yas9estBnISXcXDy98W/ZWRs= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 3eacaad6ebce6e07; Sun, 01 Nov 2026 06:59:37 +0000 X-Mizu-Trace-ID: 3eacaad6ebce6e07 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Sun, 1 Nov 2026 14:59:29 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/12] mm: hugetlb_vmemmap: unify VMEMMAP_{SPLIT,REMAP}_NO_TLB_FLUSH To: Muchun Song Cc: Muchun Song , Oscar Salvador , Andrew Morton , Mike Rapoport , Lance Yang , James Houghton , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261020115306.813483-1-songmuchun@bytedance.com> <20261020115824.823278-1-songmuchun@bytedance.com> <86d9a986-58ea-44f5-a8af-514abff12c2a@linux.dev> <99503D05-0C4D-45E4-B5D6-EDD927838935@linux.dev> From: Qi Zheng In-Reply-To: <99503D05-0C4D-45E4-B5D6-EDD927838935@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/1/26 2:56 PM, Muchun Song wrote: > > >> On Nov 1, 2026, at 14:22, Qi Zheng wrote: >> >> >> >> On 10/20/26 7:58 PM, Muchun Song wrote: >>> VMEMMAP_SPLIT_NO_TLB_FLUSH and VMEMMAP_REMAP_NO_TLB_FLUSH do not >>> describe fully independent choices. A split-only walk can defer the >>> PMD-split flush to a later global flush, and a remap-only walk can >>> defer the final remap flush. However, when a PMD split is followed >>> by PTE remapping, the split flush must happen before the PTEs are >>> changed, because stale large-page translations must not overlap with >>> new small-page translations that map different physical pages. >>> Replace the two flags with a single VMEMMAP_REMAP_NO_TLB_FLUSH flag. >>> Keep split-only walks able to defer the flush, but force the split >>> flush whenever a remap_pte callback is present. Callers that batch >>> HVO work can still defer the final remap flush and issue their own >>> global flush. >>> Current callers keep the same flushing behavior. >>> Signed-off-by: Muchun Song >>> --- >>> mm/hugetlb_vmemmap.c | 15 +++++++++------ >>> 1 file changed, 9 insertions(+), 6 deletions(-) >>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c >>> index 1105aa925acc..8b3abb562599 100644 >>> --- a/mm/hugetlb_vmemmap.c >>> +++ b/mm/hugetlb_vmemmap.c >>> @@ -42,10 +42,8 @@ struct vmemmap_remap_walk { >>> struct list_head *vmemmap_pages; >>> -/* Skip the TLB flush when we split the PMD */ >>> -#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0) >>> -/* Skip the TLB flush when we remap the PTE */ >>> -#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1) >>> +/* Skip the TLB flush while updating the vmemmap page tables. */ >>> +#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(0) >> >> Since this flag is now also used by the split-only path, the >> VMEMMAP_REMAP_NO_TLB_FLUSH name is somewhat misleading. Moreover, the >> flag does not suppress every TLB flush, as the PMD-split flush is still >> mandatory when remapping follows. > > Yeah, good point. > >> >> Would VMEMMAP_DEFER_TLB_FLUSH better describe its semantics? It > > I think so. > >> indicates that flushes which can be safely batched are deferred, without >> implying that all TLB flushes are skipped. > > I'll change it along side with the comment to: > > /* Defer safely batchable TLB flushes to the caller. */ > #define VMEMMAP_DEFER_TLB_FLUSH BIT(0) LGTM, with this change: Reviewed-by: Qi Zheng Thanks, Qi